


come between brothers

by springofviolets



Category: Voltron: Legendary Defender
Genre: Alternate Universe - Canon Divergence, Anal Fingering, Blade of Marmora Trials, Brother/Brother Incest, Everything is mostly the same except they're brothers, First Kiss, First Time, Incest, Intercrural Sex, M/M, Oral Sex, Post-Episode: s02e08 The Blade of Marmora, Sibling Incest
Language: English
Status: Completed
Published: 2019-04-21
Updated: 2019-04-24
Packaged: 2020-01-23 03:21:45
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,805
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18541258
Author URL: https://archiveofourown.org/users/springofviolets/pseuds/springofviolets
Summary: They didn't say anything about what it meant that the blade had come alive for Keith. No matter what their history held, what it might say about the blood they shared, he would always be Shiro's brother. That was exactly the problem, though it was seeming less and less like a problem to Shiro.





	1. Chapter 1

**Author's Note:**

> y'all loved brother kink so much so i was like, what if i just ... made it not just a kink. 
> 
> so this is an au where everything is mostly the same, except they actually did grow up as brothers. (also this is not meta or salt, i just think it's hot. and would be interesting.) the next chapter will be mostly the smut. ;)
> 
> thank you to [bootyshortskeef](https://archiveofourown.org/users/bootyshortskeef/pseuds/bootyshortskeef) and [bmot](https://archiveofourown.org/users/bmot) for reading over for me!

As soon as the door shuts behind him, Shiro sags against it and drops his head into his hands.

He'd liked that too much.

He shouldn't have liked that _at all._

Keith was hurt, and Shiro patched him up, just like he always has. He had helped peel the skin-tight suit down Keith's bruised and bloodied shoulders until it stopped at his waist, and Shiro knows he held his hands there, hovering near Keith's hips, for a second too long.  He applied ointment to Keith's cuts and tried not to think about the one little whimper that managed to escape Keith.

They didn't say anything about what it meant that the blade had come alive for Keith. That odd looking knife that their parents left to Keith had finally provided some kind of information, but left Shiro with more questions. But no matter what their history held, what it might say about the blood they shared, he would always be Shiro's brother.

That was exactly the problem, though it was seeming less and less like a problem to Shiro.

He palms his cock through his pants, his head thunking against the door. Maybe — maybe if he just got it out of his system. He's never thought of Keith like this before — he _hadn't, he hadn't_ — and maybe if he rides this out, it'll pass, and he can be the big brother he should be again.

Shiro had changed back into his regular clothes before tending to Keith, and he's thankful now because he can just yank his pants down far enough to pull out his cock. He was already hard, and his freed cock bobs in the air. Shiro spits into his flesh hand, and wraps it around himself.

When did Keith get so beautiful? It had struck him, when Keith found him, just how long a year really could be: the length of Keith's hair, the way he'd grown more into the angles of his face, the strength in his arms as he helped Shiro up and out of that place where the Garrison was holding him. His brother had grown, and Shiro had missed it. He'd missed who knows what else.

Now, he wonders what Keith did on his eighteenth birthday. He wonders if Keith spent it alone, if he had wished Shiro was there instead of in space. He worries about Keith, who walks the tightrope of either total lone wolf or dangerously wild. God, had he — had he gone out, anywhere, with anyone? Shiro's never asked — it hadn't seemed like the most important issue they were facing, but he thinks about it now, as he strokes his cock. Did Keith find a party for his eighteenth birthday? Did he find another boy's bed? Has he felt someone's dick other than his own?

Shiro groans, ragged, his cock hard and leaking at the thought. He slides his palm over the head, drags the slick precum with him on the downstroke as he speeds his hand up.

Shiro could have shown him. He would have looked the other way when Keith stole a sip of beer in celebration, but no more. Then he would have stripped the birthday boy, his little brother, freshly eighteen, down to his beautiful bare skin, and made sure his first time was gentle and so, so good.

But that was something Shiro hadn't thought about _then_ , for obvious reasons. He's thinking about it _now_ , and _now_ Keith is even more stunning.

"Fuck," Shiro gasps, arching off the door and into the circle of his hand.

Keith is a flame that Shiro's afraid he can't stay away from. He's the fire Shiro needs to keep warm but right now he's _too hot._ The fierceness in Keith's eyes has turned into a blaze, lighting him up inside and out. Shiro's never seen anyone more beautiful than his brother. He's never loved anyone as much, either.

With his other hand, Shiro reaches under his shirt to cup his chest, pinching at one of his nipples. God, Keith would probably be just as fiery in bed as anywhere else, even if it was his first time, even if he was a little shy about doing this with his own brother. He thinks about Keith rolling them, pinning Shiro and biting at his chest, grinding their cocks together.

He's pumping his cock hard and fast now, no longer interested in teasing himself. He needs to come, needs to feel that release, even if it's alone, not with —

"Keith," Shiro gasps out, "Keith," muscles tightening as he gets so close —

"Shiro?"

His lungs stop. His hand stops. Everything stops, suspended on the sound of Keith's voice on the other side of the door.

"Shiro," Keith repeats. He sounds level, but Shiro knows him, and he can hear the quiver underneath. "Let me in."

The situation has not softened Shiro's cock; while he's horrified at being caught, Keith's voice does nothing but make him stir even more. He tightens his fist around his cock, fighting the urge to stroke himself while Keith talks to him, and swallows down another moan.

Even though Keith surely already knows, there's absolutely no way to hide what he's doing if he lets Keith in. There's no saving this if he opens the door.

"I can't. Keith, I— you need to go," he tries, weakly.

He can hear Keith suck in a deep breath. "Shiro. I want you to trust me that's the last thing _either of us_ wants. Please, please let me in." It sounds like Keith's palm sliding against the door.

He's never been able to deny Keith anything.

Shiro shoves himself back into his pants quickly, ignoring how tight they seem. He hits the lock and steps away from the door, letting it slide open behind him.

Keith's eyes sweep over him, intense, like he's inspecting him for injury. He's wearing soft pajama pants and one of Shiro's large t-shirts, and Shiro knew this because he helped Keith into them, but it still makes his breath catch, seeing Keith in his clothes.

"Keith —" he begins.

"You're hard," Keith whispers. His eyes flick back up to Shiro's face, and he moves closer to Shiro. "Is this… is this because of me?"

With a wince, Shiro says, "I'm sorry."

"Don't be," Keith says, in that way that's only ever gentle when he talks to Shiro. "I've been getting hard-ons over you since the day I was capable of getting them at all." He lets out a little huff of a laugh at the end, like it's an embarrassing confession, like he didn't just catch Shiro moaning his brother's name.

Surprised but not, Shiro thinks of how often Keith trailed him, how fiercely Keith defended him when they were kids. How hard Keith cried when Shiro told him he was going to Kerberos, even though he tried to save it until he thought Shiro was out of earshot. He thinks of how fierce and long Keith hugged him when they found each other again — when Keith saved him — and the desperate way he begged Shiro's hologram not to leave him during the Trials.

At the time, Shiro always figured it was normal attachment for two siblings left behind by parents. Now, Shiro sees something else.

Keith's hand trails, curious and cautious, over the clothed expanse of Shiro's chest, down to his stomach. Shiro covers Keith's hand with his.

"Keith, we shouldn't. You deserve someone who…" Shiro flounders to explain, because he's not hung up on labels or taboos, not really, not when they're in space fighting aliens. They've got way bigger things to worry about, and Keith would call him on that, he knows. This is something else. "I'm sorry that I failed you by making it like this. You deserve someone to support you, especially family, that you can trust has no... ulterior motives. Not a brother who wants to — to touch you."

"Shiro," Keith says, and tilts his head up so that their lips are nearly touching. "Don't you think I'm actually the luckiest, to have one person who loves me in every possible way?"

He looks at Keith, stunned. Keith always has had a way of cutting through the bullshit everyone around him builds up, and it's no different here, because it's true: Shiro loves Keith. That's all. They love each other.

Keith is watching him, waiting, and that's the biggest sign that this is real and he's serious — the fact that he's being patient with Shiro when he could have already done something. Sometimes, to others, he knows Keith seems like a ticking time bomb, ready to go barrelling against orders, crashing off cliffs, straight into danger without a second thought.

But when it's important, when it matters, when it comes to them, Keith can be considerate and slow, just like he is now. His heart swells at the man Keith has become. It's love.

"Yeah. Me too," Shiro says, and Keith's face relaxes, revealing the beginning of a smile. "Can I —"

"You _better_ ," Keith replies, then yanks him down so their lips meet in their first kiss.


	2. Chapter 2

**Notes for the Chapter:**

> here's the final part!!

Kissing Keith isn't world-stopping, maybe, but Shiro didn't expect that. It is this: the dawning, heart-pounding revelation that this is how things have always been meant to be.

Keith's lips part, and he shivers under Shiro's hands at the first touch of their tongues. Keith's mouth tastes like a long day, the iron tang of blood underneath it, but he doesn't care. His brother presses close to him, hand fisted in Shiro's shirt as he kisses him back desperately.

Distantly, Shiro registers that he's being walked back towards the bed. The backs of his knees hit the mattress and he lets himself fall back, Keith crawling eagerly after him, not letting their mouths part for a moment. It's a shock, how Shiro has never before felt this close to being devoured just from a kiss, how he never felt this desired by anyone before Keith.

Keith kisses him, and it's wet and uncoordinated and he smushes Shiro's nose. He cradles Keith's head to tilt it, sucking at Keith's tongue, and Keith moans into it.

"Shiro," Keith whispers. His breath is damp against Shiro's cheek, and he reaches down to feel where Shiro is still hard in his pants. "I wanna touch you."

"We should — maybe slow down," Shiro stutters. He can't help the groan that comes out as Keith rubs his cock.

Keith levels him with a stare. "Why? We should do whatever feels right," he says.

He starts unbuttoning the shirt he’s wearing, and Shiro swallows as a sliver of his chest is revealed, one of his small, perfect nipples. This should be a normal sight to him, especially since he saw Keith, stripped down, less than an hour ago. But it's different when they've both admitted their affection goes way past the brotherly feelings they should have — though Shiro thinks if he tries to untangle where one feeling ends and the other begins, he wouldn't be able to — and Keith hovers over him, practically in his lap.

"Unless." Keith pauses in shrugging the shirt off his shoulders and bites his lip. "Unless it's too fast for you? I can stop."

Realizing he's just been staring, Shiro shakes his head. "No. You're just. So beautiful, Keith," Shiro breathes out. "I want you so much."

"Good," Keith says, confidence returning to his posture. "Gonna take your pants off?"

Shiro barks out a laugh at the bluntness. "Really, just my pants? Is that all I am to you?" he jokes, and it feels normal again, even if he's watching Keith pulling off the rest of his clothes.

Then Keith is in his bed, naked, all his glorious fair skin nearly glowing in the low light of the room. His cock is hard, curved up to lay against his hip. "All of it," Keith tells him. "I wanna see everything, Shiro."

He slides back over and pushes Shiro's shirt up until Shiro grabs it and tugs it the rest of the way off. He immediately starts on Shiro's pants, then, and those are off within a few more seconds. Keith seems to drink him in, smoothing his hands over the planes of Shiro's chest.

"I know I look a little different than the last time we saw each other naked," Shiro laughs, just a little self-conscious. He knows he's attractive, and has plenty of evidence that Keith thinks so, but it still makes him hyper-aware of his body. No one's seen him like this since Adam, and Keith probably hasn't seen him fully nude since they were kids.

"Yeah," Keith agrees, face stoic. His hands trail down, and he gives Shiro a cheeky grin as he strokes him. "For one, your cock is way bigger."

His cock jerks in Keith's grip. " _Keith_." The hand on his cock is what sends this crashing from dream to reality, makes Shiro slam back into his body fully and think _This is real. We're doing this._ He breathes in deeply. "Did you — how do you know, did you get a good look at it before, then?"

"Way too many times," Keith tells him. He mouths at Shiro's neck, open-mouthed, wet kisses scattered on his skin, as he pumps his cock steadily. Shiro grabs his hair and pulls Keith's head back so he looks at Shiro, purple eyes glittering. "Told you. I've wanted you for a long time, Shiro. Of course I'd sneak a look when my hot big brother gets out of the shower, or…"

Shiro thinks of Keith watching him when they were both at the Garrison, wonders if Keith snuck back to his room the same way Shiro had today, hard and wanting, jerking himself off to the thought of his older brother. What did Keith imagine, in his teenage fantasies? Shiro thinks. _Fuck_. This is his little brother. But — Keith obviously doesn't care, and if Shiro is truly honest with himself, if he also admits this isn't the very first time he's considered Keith like this, neither does he.

"You have no shame," Shiro says, mostly in wonder. Keith has always been half-wild, so uncaring of convention that it's like he doesn't even know certain rules exist. Shiro's always loved that in him, and now even more, when it grants them the space for this.

Keith practically purrs as he bucks his hips down into Shiro. "It's you, Shiro. There's no shame in wanting you."

Shiro leans up to kiss Keith again, and he thinks he's already addicted to this, to Keith's lips against his and his body under his hands. His skin is so smooth except for where Shiro had placed bandages earlier, and Shiro gentles his touches until Keith is shivering from the way they ghost down over his sides. "And now you have me," Shiro says, running his hands back up Keith, over his toned stomach, and rubbing thumbs over his nipples. "What do you want now?"

"Uh," Keith starts, and he closes his eyes, long black eyelashes fluttering over his pink cheeks. "I haven't really done anything before? But I want _this_ in me," he says, grinding back on Shiro's hard cock, which slides along the crease of his ass.

The breath has been knocked from Shiro so many times tonight. "You're a virgin," he says, trying hard not to dig his fingers into Keith from how much this turns him on. Keith is a fantasy come to life, and still so much more; he's everything Shiro could dream of, from the only person he'd truly want it from.

Keith rolls his eyes. "Yeah, obviously, but I know what I want." He rotates his hips, his cock leaks precum onto Shiro's chest. Shiro wants to lick it where it beads at the tip. "Fuck your little brother, Shiro. I need you."

"Baby." The word slips out in a groan, and Keith whines. "Oh. You like that, baby?" he asks, and for the first time since Keith pushed his way into the room and laid all their feelings out, Shiro feels back in control. "I'm not going to fuck you tonight. Considering your injuries, I almost want to send you back to your room, but —"

With something akin to a growl, Keith reaches back and pulls one of his ass cheeks, letting Shiro's cock slip further between them. "C'mon, Shiro, no, I _want_ it."

"Shh," Shiro soothes. He caresses his palms over the sweet roundness of Keith's ass. "We'll get there, but I want to go easy on you tonight. Here, roll over." He shifts them over so Keith is on his side with the non-injured shoulder; after a quick check of the drawers next to his bed for lube, he spoons him from behind. He skims his fingers down Keith's thighs, loving the way they're soft but strong, the fuzz of the hair on them.

 _Yes,_ this will be _perfect._

He nuzzles the back of Keith's neck. "I want to fuck your thighs," Shiro explains. "Is that okay?" Keith nods vigorously, wiggling his ass back against Shiro. He laughs softly and presses a kiss to Keith's hair, then drizzles some lube out of the bottle.

"Oh," Keith moans when Shiro coaxes his cock between Keith's thighs. He has them pressed together, but not too tight. His skin is warm. Shiro gives a small thrust forward, and his cock brushes Keith's balls. "Oh, _fuck_!"

"That good?" he asks in Keith's ear. "Keep them closed, baby," he adds when Keith shifts and the grip of his thighs loosens. Shiro wraps his metal arm around Keith's front to pull him closer, rocking into the space Keith makes for him. One day he'll sink into Keith's tight hole, maybe, but god, he really loves Keith's thighs, dizzy with how much smaller but how strong they are.

Keith tilts his head back so it rests on Shiro's shoulder and squeezes his legs together; the hot, slick grip of his thighs flex around Shiro's cock. "Mmm. _Shiro_." He reaches behind himself to grab at Shiro's ass and hold him tight, moving in sync with Shiro's thrusts.

Shiro's other arm strokes down Keith's just to brush over Keith's cock where it lays hard and dripping against his belly. He trails a fingertip over the leaking tip. Keith gasps against when he moves further down to cup Keith's balls, and he can feel the head of his own cock pushing through beneath them.

"God, Keith. You feel so good." He quickens his pace, fucking into Keith's thighs erratically.

"You too," Keith gasps, reaching for his own cock. "Shiro. You're so big, _ah_ , just like I imagined —"

With a choked groan, Shiro comes between Keith's thighs. His come spurts over Keith's balls, dripping down the backs of his thighs as Shiro pulls back.

"No, come back," Keith demands. "I want you to fuck me, I want your cock. _Shiro_."

He pets Keith's side as he turns him carefully onto his back. "I already told you not yet," he chides. "But if you need something in you, ask nicely." He scoots down the bed a few inches and dips his head to lap at the head of Keith's cock.

"Shiro, please," Keith whines, squirming. He attempts to glare, but it's without any heat. "You're my brother. I love you. Please fuck me or _something_."

Shiro groans. " _Brat_." He wasn't planning to deny Keith, but Keith still has to prove just how easily Shiro will give him anything. He knows how to get it, how to pull at all Shiro's love for him, and has learned, all too quickly, to stoke the lust right along with it. He drags his fingers through the thick come on Keith's thighs, coating them. "Spread your legs for me, baby."

With a pleased grin, Keith obeys, his thighs parting sweetly; he even draws his legs up.

Shiro watches Keith's face closely as he rubs a wet finger over Keith's hole. Keith puffs out a breath of anticipation, eyelashes fluttering, brows drawing in just the slightest. He may not have said as much, but Shiro suspects Keith hasn't even done this before, and even if he had, Shiro's fingers are twice as thick. He starts with just the one, and makes sure the first press of his finger is slow.

Keith's lips part on a moan when Shiro's finger sinks smoothly inside him, and his eyes snap open. " _Ahh_! Oh, god, Shiro. _Ohh_ —"

On his stomach, Keith's cock is twitching, flushed red and leaking big drops of precum. "Is that good?" he asks.

"Yes," Keith growls. "More, fuck, Shiro, please —"

Shiro pumps his finger a few times, then withdraws. He scoops up more come from Keith's thighs, sliding two fingers inside Keith this time.

Keith arches and shouts. " _Shiro_! Oh, please, ah, feels so full and good, Shiro, Shiro —"

Leaning down again to lap at the crown of Keith's cock, Shiro works his fingers in and out of Keith, curling his fingers on each stroke out. Keith spills precum over Shiro's tongue, and Shiro swallows eagerly, suckling at the head as his fingers fuck into Keith.

" _Ahhh_ , fuck!" Keith sobs, grabbing at Shiro's hair as he clenches around his fingers and comes into his mouth.

Shiro swallows it all down, spreading his hands across the backs of Keith's thighs, feeling them tremble under his touch as he licks Keith's belly clean. Keith's grip on his hair gentles, and Shiro looks up at him.

"I can't believe I came so quick," Keith says, a sweet blush on his cheeks. "I'll last longer next time."

"I didn't mind it," Shiro replies, kissing the corner of his mouth. "Besides." He glances back at Keith's cock, and says, teasing, "Looks like you have a recovery time that more than makes up for it."

He laughs breathlessly into Shiro's neck. "Yeah. Maybe it's a… nevermind," he says, trailing off. His tone is thoughtful but sleepy, and Shiro assumes they'll be waiting to put that recovery time to use. "Hey, Shiro. I really love you."

"I love you too, Keith. So much." He brushes Keith's hair back from his face, his heart stuttering from how beautiful Keith looks.

Keith's breathing turns soft, and Shiro keeps stroking his hair as he listens to Keith fall asleep.

In the morning, they can talk about what to do long-term. Their family relationship was always kept quiet at the Garrison; combined with recent events, the team could believe they were never anything more than mentorship turned close friends. If Keith wants that, Shiro will do it.

But for now, all he needs to worry about is cleaning them up without waking Keith, and making sure Keith doesn't drool too much on his pillow.

Even if he does look adorable, Shiro thinks fondly, and presses his lips to Keith's forehead in a silent kiss.

**Author's Note:**

> Kudos/comments are loved!
> 
> This story is part of the [LLF Comment Project](https://longlivefeedback.tumblr.com/llfcommentproject) (including the [LLF Comment Builder](https://longlivefeedback.tumblr.com/post/170952243543/now-presenting-the-llf-comment-builder-beta)), which was created to improve communication between readers and authors. This author invites and appreciates feedback, including:
> 
>   * Short comments
>   * Long comments
>   * Questions
>   * “<3” as extra kudos
>   * Reader-reader interaction
> 

> 
> This author responds to comments.
> 
> -
> 
> you can also find me on [twitter](https://twitter.com/springofviolets).
> 
> edit: [FANART BY CARPINCHO_KEV HERE](https://twitter.com/Carpincho_Kev/status/1122249419754213382)!!!! thank you sooo much omg ❤❤❤


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